1. Field of the Invention
The present invention relates to an apparatus and method for processing food products in a heat exchanger. Although suitable for many types of hot and cold food products, the apparatus is described in connection with frozen confections such as soft-serve sorbets and yogurts, for which it has particular advantages.
2. Description of the Related Art
Bacterial contamination is a significant concern with related art food processing machines. A typical related art commercial frozen confection machine contains four integrated systems; an insulated compartment for storing liquid food substances; a gas circuit for providing an edible gas for mixture with the liquid food substances; a production unit for making a frozen confection from the mixture of liquid and gas; and a refrigeration circuit for cooling both the insulated compartment and the production unit. If bacteria is able to enter the frozen confection machine through any one of these systems, health hazards may occur.
Many related art machines are open system devices wherein liquid food product is poured into an opened holding reservoir or is otherwise exposed to air from the surrounding atmosphere. Such structure not only increases the possibility that bacteria and foreign particles will contaminate the food product, but also allows odors in the surrounding atmosphere to be absorbed into the food product, degrading the taste of the end product. Many hospitals and other institutions that use odorous sanitizing chemicals avoid frozen confection machines in their cafeterias for this very reason.
In addition, the storage compartment is typically connected to the production unit by a tube which defines a food path. In order to minimize bacterial contamination within the system, it is desirable to minimize the length of the food path and the number of components through which the liquid food substance must pass before it is frozen in the production unit. However, even when shortened, nooks and crannies in the conventional food path provide a haven for bacterial growth. Therefore, related art machines must be flushed, disassembled, sanitized, and reassembled on a daily basis to avoid hazardous contamination- However, this cleaning operation is time consuming and often results in wasted food product.
A maintained positive system pressure is also critical to a bacteria free environment. While related art devices may use pumps to convey liquid food substance into a production unit, they may not be designed to always maintain a positive pressure in the system during use. Rather, they may fluctuate between positive pressure and atmospheric pressure, or may substantially operate at atmospheric pressure. If the pressure in the system falls to atmospheric pressure, contaminants may enter the system leading to bacterial growth. Thus, more frequent cleaning may be necessary to maintain a bacteria free environment.
Another problem with related art devices is their limited ability to control the uniform quality of their end product. The present inventors have recognized that there exists a direct relationship between the pressure within the heat exchanger and the resulting quality of the end product. Critical pressures vary depending upon the make-up of the food product and food product temperatures. However, in the related art, precise control of system pressure is difficult. In addition, the goal of keeping the food path free of elements that define nooks and crannies that permit bacterial growth, discourages the use of conventional pressure sensors within the system.
It is also important to precisely control the proportion of food product and gas entering the production unit in order to ensure the quality and consistency of the end product. Desired proportions may vary depending upon the make-up of the food product being used as well as control standards. However, related art devices lack the ability to precisely control the proportion of gas and food product that is sent to the production unit.
Finally, temperature control is also important to the quality of the end product. As the liquid food substance cools in the production unit, its ability to absorb and be become emulsified with the gas decreases. Thus, if a critical temperature is reached before the gas and liquid are fully emulsified, pockets of gas will form in the heat exchanger. When a dispensing valve on the production unit is opened, these pockets of gas may "blow-out," spewing-food product through the valve. In addition, product quality may be poor if full gas emulsification has not occurred.
In order to prevent blow-outs and to provide a fully emulsified product, the cooling rate may be decreased. However, the slower the mixture cools, the larger the crystal size in the end product. Since smaller crystal size results in a smoother textured end product, a fast cooling rate is desirable.
Some related art devices separately inject the liquid and gas into the production unit, and some include premixing units or saturators in the food path for mixing the liquid and gas before it enters the cooled environment of the production unit. A drawback of premixing units is that they provide additional nooks and crannies within the food path that may trap food particles and thereby lead to bacterial growth.
Thus, a major drawback of related art devices is their inability to accurately control pressure, temperature and the ratio of food substance to gas, while at the see time maintaining a virtually bacteria free environment.